This disclosure relates to silencers, such as mufflers. In particular, this disclosure relates to methods and arrangements for mufflers, which, in addition to normal attenuation duties, are particularly useful for silencing the types of noise associated in the cab environment of a truck, especially a heavy duty truck.
In the trucking industry, there is greater attention being paid to the comfort of the driver. The trucking industry typically uses heavy duty engines, on the order of a horsepower of 300-600 HP. These engines are typically noisy, emitting sound pressure levels on the order of 89-104 dB(A) at full throttle.
Because of the noise produced by these engines, there have been muffler arrangements of various types developed to reduce this noise. There are regulations to require noise abatement produced by heavy duty engines. By-and-large, the focus of these regulations has been directed to xe2x80x9cdrive-byxe2x80x9d conditions. That is, the noise is measured from a position that is a set distance away from and external to the truck.
The cabs in trucks have been changing over the years to accommodate sleeping quarters. In some instances, the trucks are driven by a team, such that while one person is driving, the other person is resting or sleeping in the sleeping quarter of the cab. Thus, the noise level in the cab needs to be low enough to permit comfort for both the driver and for the team member who is resting.
Silencers or muffler arrangements are described that, in certain preferred situations, are particularly useful for attenuating low frequency noise associated with the internal volume of cabs or sleepers in heavy duty trucks. In general, muffler arrangements described herein have an outer wall defining an internal volume; an inlet tube oriented at least partially within the internal volume; an outlet tube construction oriented at least partially within the internal volume and including a diverging section and a choke extension; and a first baffle structure securing the outlet tube construction within the internal volume. Muffler arrangements constructed according to principles described herein will have xe2x80x9cextended chokes.xe2x80x9d In other words, in preferred constructions, a ratio of the diverging section axial length to the choke extension axial length is preferably less than 3:1. In many preferred embodiments, the first baffle structure defines an aperture arrangement therein to permit gas flow communication therethrough.
Methods of muffling heavy duty trucks and of installing mufflers will preferably utilize mufflers constructed according to principles described herein.